Prospective study of dietary patterns and persistent cough with phlegm among Chinese Singaporeans

Rationale: Using principal components analysis to examine dietary patterns complements the evaluation of individual food and nutrient intake in relation to health outcomes, but has not yet been applied to nonmalignant respiratory disease or symptoms. Objective: To examine the relation between patterns of dietary intake at baseline and new onset of persistent cough with phlegm in a population-based cohort of Singapore Chinese. Methods: A 165-item validated food frequency questionnaire was administered in-person at baseline in 1993. We identified 623 cases of incident cough with phlegm among 52,325 subjects by telephone interview from 1999 through 2004. We identified two distinct food patterns: a meat-dim sum pattern characterized by pork and chicken dim sum foods and noodle dishes, and a vegetable-fruit-soy pattern characterized by vegetables, fruit, and soyfood items. Main Results: The meat-dim sum pattern was positively associated with new-onset cough with phlegm (odds ratio, 1.43; 95% confidence interval, 1.08, 1.89; comparing fourth to first quartile, p for trend = 0.02), after adjustment for age, sex, total energy intake, smoking, education, and nonstarch polysaccharide intake, a protective factor for cough with phlegm in this cohort. Weaker associations were seen for more chronic symptoms and for incident asthma. A weak inverse association for the vegetable-fruit-soy pattern disappeared after adjustment for nonstarch polysaccharide intake. Conclusion: A diet rich in meats, sodium, and refined carbohydrates may increase risk of developing cough with phlegm, independently of the apparent beneficial effects of a diet high in fiber in this Singapore Chinese cohort.